The present relates to a substantially anhydrous blowing agent and a process for producing the same.
Blowing agents, such as azodicarbonamide, have been conventionally utilized extensively for thermoplastic resins, for example, vinyl chloride resins, polyolefin resins (polyethylene resins, polypropylene resins, and the like), ethylene vinyl alcohol resins, rubbers, and the like.
These blowing agents, which are usually finely powdered compounds, have a problem that they aggregate and are solidified with the lapse of time or under load to thereby show impaired flowability in the step of addition to resins to cause hopper clogging, or to thereby have impaired dispersibility into resins. Mitigation of this solidification is desired more and more with the recent trend toward quality improvement in foamed resins and labor saving in the production thereof.
Techniques currently employed for overcoming the above problem include (1) technique of adding inorganic powder particles, such as silica, metal silicate or the like, as a solidification inhibitor to a blowing agent, (2) technique of batchwise drying a blowing agent for a sufficient period to thereby diminish the water contained therein in a slight amount, and the like.
However, use of these techniques has various drawbacks. Namely, technique (1), although effective in solidification prevention in some degree, cannot impart the effect which lasts beyond several months. For application to a blowing agent comprising finer particles, inorganic powder particles should be added in a larger amount. However, the addition of a larger amount of the inorganic powder particles is causative of cell enlargement during foaming, and is hence undesirable in applications where fine cells are required. Technique (2), on the other hand, has significantly reduced productivity because the drying requires much time, resulting in an increased production cost. In addition, technique (2) cannot cope with continuous production. Furthermore, it is difficult to dry and remove the water contained in crystals sufficiently to thereby obtain a substantially anhydrous blowing agent. Also, effects in solidification prevention is limited.
Japanese Published Unexamined Patent Application No. 320432/92 discloses a method of adding a silane coupling agent dissolved in a solvent to azodicarbonamide to thereby improve flowability and dispersibility into resins. However, this method is ineffective in sufficiently preventing solidification.
Furthermore, Japanese Published Unexamined Patent Application No. 295872/96 discloses a method of adding an aluminum coupling agent dissolved in a solvent to a chemically blowing agent to thereby improve flowability and dispersibility into resins. However, this method is also ineffective in sufficiently preventing solidification.
The present inventors made intensive studies in order to eliminate the above problems. As a result, they have-found that a substantially anhydrous blowing agent is obtained by treating a blowing agent with a surface-treating agent capable of removing water from the blowing agent, and optionally by heating it. Furthermore, they found that the blowing agent thus obtained is significantly inhibited from solidification and is exceedingly useful as a blowing agent satisfactory in flowability, dispersibility into resins, and the like, even after the lapse of a prolonged period of time. The present invention has been completed based on these findings.
That is, the present invention relates to a substantially anhydrous blowing agent, especially a substantially anhydrous crystalline azodicarbonamide.
Furthermore, the present invention relates to a substantially anhydrous blowing agent obtained by treating a blowing agent with a surface-treating agent capable of removing water from the blowing agent.
Moreover, the present invention relates to a process for producing a substantially anhydrous blowing agent, which comprises treating a blowing agent with a surface-treating agent capable of removing water from the blowing agent under conditions substantially free of a solvent.
The substantially anhydrous blowing agent of the present invention has been significantly improved especially in unsusceptibility to solidification under load and in unsusceptibility to solidification with the lapse of time. Hence, the substantially anhydrous blowing agent is extremely free from solidification even through long-term storage in a stacked state, and retains for a long time the satisfactory flowability and the satisfactory dispersibility into resins which properties are possessed by the crystalline powder immediately after production.
The foaming performances of the blowing agent of the present invention are equal to those of the conventional blowing agents.
Consequently, as a result that the substantially anhydrous blowing agent of the present invention is provided, the fear that blowing agent products may be solidified under load or with the lapse of time from the production thereof to the use thereof by users is eliminated.
The blowing agent which can be used in the present invention is selected from conventionally known blowing agents. Examples include azodicarbonamide (ADCA; decomposition temperature: about 200xc2x0 C.), p,pxe2x80x2-oxybis (benzenesulfonyl hydrazide) (OBSH; decomposition temperature: about 160xc2x0 C.), dinitropentamethylenetetramine (DPT; decomposition temperature: about 200xc2x0 C.), p-toluenesulfonyl hydrazide (TSH; decomposition temperature: about 110xc2x0 C.), benzenesulfonyl hydrazide (BSH; decomposition temperature: about 95xc2x0 C.), and the like.
The present invention can be advantageously applied especially to blowing agent powders having a decomposition temperature of 100xc2x0 C. or higher. Particularly, much merit is brought about when the present invention is applied to ADCA, in which solidification has conventionally been a serious problem.
The blowing agent in the present invention is preferably in the form of a powder. Although the particle diameter thereof is not particularly limited, it is generally about 1 to 50 xcexcm, preferably about 3 to 30 xcexcm. The term xe2x80x9cparticle diameterxe2x80x9d as used herein means the median size determined with a laser diffraction particle diameter distribution analyzer.
The term xe2x80x9csubstantially anhydrousxe2x80x9d as used herein means to have a water content lower than 0.03% by weight, preferably lower than 0.010% by weight. The water content (% by weight) in crystalline ADCA is herein determined by heating the crystalline ADCA at 110xc2x0 C. for 2 hours while passing water-free nitrogen gas therethrough, introducing the effluent nitrogen gas into a Karl Fisher""s water meter (trade name: MKS-1; manufactured by Kyoto Electronics Manufacturing Co., Ltd.) prevented from suffering water penetration thereinto from the surrounding air to measure the amount of water contained in the nitrogen gas, and converting this water amount into a percentage amount based on the weight of the crystalline ADCA.
The surface-treating agent which can be used in the present invention is one capable of removing water from a blowing agent Examples include compounds having the property of chemically reacting with water and compounds having the property of adsorbing or holding water. Specific examples include coupling agents, organic acid anhydrides, anhydrous inorganic compounds, desiccants, and the like.
Examples of the coupling agents include silane coupling agents, aluminum coupling agents, titanate coupling agents, and the like.
Examples of the silane coupling agents include conventionally known silane coupling agents. Specific examples include methyltrimethoxysilane, xcex3-aminopropyl-triethoxysilane, N- (xcex2-aminoethyl) -xcex3-aminopropyl-trimethoxysilane, N-phenylaminomethyltrimethoxysilane, vinylmethyldiethoxysilane, and the like.
Examples of the aluminum coupling agents include conventionally known aluminum coupling agents. Specific examples include aluminum isopropylate, aluminum ethylate, aluminum tris(ethylacetoacetate), ethylaceto-acetatoaluminum diisopropylate, and the like.
Examples of the titanate coupling agents include conventionally known titanate coupling agents. Specific examples include isopropyl triisostearoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, bis(dioctyl pyrophosphate) hydroxyacetate titanate, and the like.
These coupling agents can be used alone or as a mixture of two or more thereof. Among these, preferred are aluminum coupling agents, particularly, aluminum tris(ethylacetoacetate).
Examples of the organic acid anhydrides include conventionally known organic acid anhydrides. Specific examples include phthalic anhydride, succinic anhydride, glutaric anhydride, benzoic anhydride, trimellitic anhydride, and the like these compounds bond to and remove water in a blowing agent, for example, by the following mechanism:
(RCO)2O+H2Oxe2x86x922RCOOH
(wherein R represents an organic acid residue).
The above coupling agents and the organic acid anhydrides can be especially preferred because they not only have the property of chemically reacting with water to thereby remove the water contained in a blowing agent, but also have the property of forming a film capable of preventing external water absorption on the surface of the blowing agent (for example, unreacted coupling agent, and the like).
Examples of the anhydrous inorganic compounds include known anhydrous inorganic compounds so long as they can remove crystal water by binding to water. Specific examples include anhydrous magnesium sulfate, anhydrous potassium carbonate, anhydrous sodium carbonate, anhydrous sodium sulfate, anhydrous sodium sulfite, anhydrous magnesium carbonate, and the like. These compounds adsorb water contained in a blowing agent and fix the adsorbed water as crystal water, for example, by the following typical mechanism:
Na2SO4+nH2Oxe2x86x92Na2SO4.nH2O
(wherein n represents an integer of 1 or more).
Examples of desiccants include conventionally known desiccants so long as they have the property of removing water. Specific examples include acid clay, silica gel, magnesium oxide, calcium oxide, and the like.
In the present invention, the coupling agents, the organic acid anhydrides, the anhydrous inorganic compounds, and the desiccants may be used alone or as a mixture of two or more thereof as the surface-treating agent.
Upon application to the surface of a blowing agent and-preferably heating, the surface-treating agent efficiently reacts with or adsorbs water contained in the blowing agent to thereby reduce the water content of the blowing agent.
The surface-treating agent is preferably used as it is without being dissolved in a solvent, preferably under conditions substantially free of a solvent, in order that no adverse influence be exerted on reaction with water or adsorption of water. If a solution or dispersion of an coupling agent in a solvent is used, the reaction between the water present in the blowing agent and the coupling agent does not proceed sufficiently, water is remained in the blowing agent, and therefore, a substantially anhydrous blowing agent cannot be obtained. Consequently, such use is not preferred under the mixing conditions where pulverization of a blowing agent is inhibited. Especially, use of an organic solvent containing water or moisture is not preferred because a water content in the blowing agent may be increased to the contrary.
The term xe2x80x9cunder conditions substantially free of waterxe2x80x9d as used herein means that no solvent is used or that an organic solvent containing a water content of less than 0.1% by weight is used in an amount equal to or less than the amount of the surface-treating agent. In the case of using a solid surface-treating agent, it is preferably used in the form of a fine powder or after being melted.
The amount of the surface-treating agent per the blowing agent varies depending on the amount necessary for allowing the surface-treating agent to react with the water content contained in the blowing agent. Specifically, the surface-treating agent is generally used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 0.5 parts by weight, based on 100 parts of the blowing agent.
In the present invention, heating treatment is preferably conducted during or after the addition of a surface-treating agent to a blowing agent to thereby accelerate the reaction between the water in the blowing agent and the surface-treating agent. In the present invention, the heating treatment conducted during or after the treatment of a blowing agent with a surface-treating agent is particularly referred to as xe2x80x9ctreating and heatingxe2x80x9d.
It is effective that the heating is carried out during the addition of a surface-treating agent to a blowing agent.
In the case of using a surface-treating agent which is solid at ordinary temperature, the surface-treating agent is preferably subjected to preheating treatment-prior to the addition thereof to a blowing agent so that the solid surface-treating agent is brought into a melted state.
For example, the heating temperature is generally from 30xc2x0 C. to the decomposition temperature of the blowing agent, preferably from 40xc2x0 C. to the decomposition temperature of the blowing agent. If ADCA, OBSH, DPT or the like having a decomposition temperature of 150xc2x0 C. or higher is used as a blowing agent, the preferred temperature is 55 to 100xc2x0 C. From the standpoint of reducing the heating period to conduct the mixing even more efficiently to thereby minimize the energy cost, it is preferred to use a heating temperature of about 70 to 90xc2x0 C.
Methods for adding a surface-treating agent to a blowing agent are not particularly limited. However, a preferred method is to spray the surface-treating agent with a pressure nozzle, a two-fluid nozzle, or the like so as to add the surface-treating agent in the form of fine droplets.
Also, preferably, the addition is carried out while sufficiently mixing a blowing agent.
Mixing apparatuses which can be used for the above mixing are not particularly limited. Examples include a supermixer, a Henschel mixer, a screw mixer such as a Nauta mixer, a proshear mixer, and a ribbon blender.
If a blowing agent which has been made substantially anhydrous is pulverized, the resultant powder has an increased specific surface area and hence enhanced hygroscopicity. Additionally, even if the blowing agent powder which has been coated to inhibit moisture adsorption is used, a section having no coating is provided, and hence hygroscopicity is increased more and more. Thus., the effect of the present invention may be lost. Particularly, if the blowing agent powders having a particle diameter of 10 xcexcm or more which are easily pulverized are used, it should be especially paid attention to this point.
Accordingly, in the present invention, preferably, the mixing is conducted under mixing conditions where pulverization of a blowing agent is inhibited. Herein the term xe2x80x9cunder mixing conditions where pulverization of a blowing agent is inhibitedxe2x80x9d means that an increase in the specific surface area through the treatment is 20% or less, more preferably 10% or less. Preferably, as mixers satisfying the conditions, mixers used for blowing agent powders having a particle diameter of about 10 to 300 xcexcm include a Nauta mixer, a proshear mixer (the chopper blades are removed before use), and the like. Furthermore, mixers used for blowing agent powders having a particle diameter of about 3 to 10 xcexcm which are comparatively difficult to be pulverized include a universal mixer, a proshear mixer (the chopper blades are removed before use), and the like. Mixers used for blowing agent powders having a particle diameter of about 3 to 5 xcexcm which are difficult to be pulverized include a supermixer, a Henschel mixer, and the like. The mixing conditions where pulverization of the blowing agent is inhibited can be provided by adjusting the rotary number of each mixer appropriately.
In using a liquid surface-treating agent, it is preferred to use a pressure nozzle, a two-fluid nozzle, or the like, to spray the surface-treating agent in the form of fine droplets over a blowing agent. By spraying a surface-treating agent as fine droplets over a blowing agent, the blowing agent according to the present invention can be obtained with a small amount of the surface-treating agent.
The substantially anhydrous blowing agent of the present invention can be advantageously used as a blowing agent for various synthetic resins in the same manner as conventional blowing agents.
Furthermore, the substantially anhydrous blowing agent of the present invention can be used as a blowing agent composition comprising the crystalline powder and one or more ingredients known in this field, such as a stabilizer, a pigment/filler, a blowing inhibitor, and the like. Examples of the stabilizer include tribasic lead sulfate, dibasic phosphites, lead stearate, zinc stearate, zinc carbonate, zinc oxide, barium stearate, aluminum stearate, calcium stearate, dibutyltin maleate, urea, and the like. Examples of the pigment/filler include chrome yellow, carbon black, titanium dioxide, calcium carbonate, and the like. Examples of the blowing inhibitor include maleic acid.
For easily understanding the present invention, a blowing agent according to the present invention obtained using ADCA as a blowing agent and aluminum tris(ethylacetoacetate) as a surface-treating agent will be explained below with respect to the effects thereof which the present inventors have ascertained. However, the following explanation should not be construed as limiting the scope of the invention in any way.
Powders of blowing agents, for example, ADCA, are usually composed of microscopically porous particles, in each of which water is present on the surface thereof and in the pores and inner parts thereof. When such a powder of ADCA is treated with aluminum tris(ethylacetoacetate), it is considered that the aluminum tris (ethylacetoacetate) reacts with the water present on the surface and in the pores of the ADCA to decompose into aluminum hydroxide and ethyl acetoacetate, and an aluminum hydroxide film is coated on the surface of the ADCA. If the reaction is carried out at a temperature as low as room temperature, a long time is required for the reaction. However, if it is heated to about 80xc2x0 C., the reaction is accelerated and completed shortly. 
It is considered that not only water is removed from the surface and pores of the powders by the above treatment, but also the water remaining in the powders in a slight amount is inhibited from migrating to the powder surface by the film of aluminum hydroxide formed, whereby solidification is prevented. The aluminum coupling agent remaining unreacted is considered to contribute to solidification prevention due to its water repellency. If the powder is further contacted with external water, the above reaction proceeds gradually and water is removed so that solidification is prevented.